_onClick: function(/*Event*/ evt){
var original = this.checked;
this._set('checked', !original); // partially set the toggled value, assuming the toggle will work, so it can be overridden in the onclick handler
var ret = this.inherited(arguments); // the user could reset the value here
this.set('checked', ret ? this.checked : original); // officially set the toggled or user value, or reset it back
return ret;
},